A plurality of antennas is installed in a transmitting end and a receiving end of a MIMO system. During signal transmission, the transmitting end transmits a plurality of independent signals through different transmitting antennas by using space division multiplexing technology, and the receiving end receives the signals from different receiving antennas and obtains the signal transmitted from the transmitting end from the received signals.
In the MIMO system, the transmitting end may use a mono-codeword or multi-codeword space division multiplexing manner to transmit signals. In the mono-codeword manner, multiple antenna signals transmitted from the transmitting end are code-modulated using the same code modulation manner; and in the multi-codeword manner, the multiple antenna signals transmitted from the transmitting end are code-modulated using two or more code modulation manners.
In the prior art, a receiving end of a multi-codeword MIMO system detects the signal transmitted from the transmitting end from the received signals mainly through three methods: Maximum Likelihood (ML), Zero-Forcing (ZF) and Minimum Mean-Squared Error (MMSE).
The detecting principle of the ML detecting method is as follows: a channel matrix is estimated, and a probably received signal vector is obtained according to the estimated channel matrix and the known signal vector probably transmitted from the transmitting end; and an actually received signal vector is compared with the probably received signal vector, a signal which is closest to the signal in the probably received signal vector is obtained from the actually received signal vector, and the signal is used as the detected signal transmitted from the transmitting end.
The error between the signal detected through the ML detecting method and the signal transmitted from the transmitting end is small. However, in the implementation of the present invention, the inventor finds that the number of calculations of the ML detecting method is large when the number of the transmitting antennas and the receiving antennas is large, thus causing complex implementation of the ML detecting method.
The detecting principle of the ZF detecting method is as follows: a channel equalization matrix is obtained according to a channel matrix, in which the product of the channel equalization matrix and the channel matrix is a unit matrix; and a signal transmitted from the transmitting end is generated according to the channel equalization matrix and an actually received signal matrix.
Compared with the ML detecting method, the ZF detecting method requires a smaller number of calculations and is easier to implement. However, in the implementation of the present invention, the inventor finds that, the ZF detecting method causes an increase of the noise power in the process of calculating the channel equalization matrix, and especially when the channel quality is poor (severely ill-conditioned channel matrix), the noise has an obvious effect on the quality of the detected signal, thus resulting in a large error between the signal transmitted from the transmitting end that is obtained through the ZF detecting method and the signal actually transmitted from the transmitting end.
The detecting principle of the MMSE detecting method is basically the same as the detecting principle of the ZF detecting method, and the difference lies in that when a channel equalization matrix is calculated through the MMSE detecting method, the estimation of the channel noise power is added, and the effect of noise and interference is taken into consideration.
Since the MMSE detecting method takes the effect of the noise into consideration, the quality of the signal obtained through the MMSE detecting method is better than the signal obtained through the ZF detecting method. However, in the implementation of the present invention, the inventor finds that, compared with the signal obtained through the ML detecting method, the signal obtained through the MMSE detecting method still has a large error from the signal actually transmitted from the transmitting end, and the error is obvious when the channel quality is poor (severely ill-conditioned channel matrix).